1. Field of the Invention
The present invention generally relates to an improved apparatus for chemical vapor deposition, and more particularly to an improved injector for use in such apparatus.
2. Description of the Prior Art
Chemical vapor deposition (CVD) and low pressure chemical vapor deposition (LPCVD) are well known and widely used processes for forming thin films in the semiconductor industry. FIGS. 1 and 1A illustrate one type of prior art apparatus for forming CVD and LPCVD films on semiconductor wafer surfaces, such films as aluminum oxide (Al.sub.2 O.sub.3) or tungsten films for example. In this prior art apparatus, a single injector indicated by the general reference numeral 12 is located directly in front of a susceptor 14 and injects a vapor into a chamber 15. Undeposited vapor exists through a port 16 on the opposite side of the susceptor from the injector 12.
The injector 12 has a generally unrestricted angular passage 18 through which vapor flows from a plenum 20 into the chamber 15. A passage 11 connects the plenum to an external vapor supply. The passage 18 is formed between an outer ring 22 and a central cylindrical member 24 that has a flat surface 25 forming a wall in front of the susceptor 14. The outer edge of the passage 18 is coextensive with the outer periphery of the wafer held by the susceptor 14. The dashed arrows in the figure show generally the vapor flow path that applicants have determined exist for this prior art design, including recirculation cells.
The apparatus of the type illustrated in FIG. 1 can exhibit certain shortcomings: namely, poor film uniformity across the surface of a single wafer; possible particulate generation; low vapor reaction efficiency; and low film deposition rates.
Additional prior art reactors and their injectors are disclosed in the following U.S. patents.
U.S. Pat. No. 4,807,562, to Sandys, discloses a chemical vapor deposition (CVD) reactor including a vertically mounted multi-sided susceptor with means to adjust the gas flow across the width of each susceptor face.
U.S. Pat. No. 4,909,914, to Chiba et al., discloses a CVD reaction apparatus which comprises a flow control system provided with a convergent-divergent nozzle.
U.S. Pat. No. 4,989,541, to Mikoshiba et al., discloses a thin film forming apparatus including, in addition to a material gas nozzle, a control gas nozzle for jetting a control gas flow which encircles a material gas flow jetted from the material gas nozzle against a substrate supported in a reaction chamber, so as to shape the material gas flow into the form of a beam.
U.S. Pat. No. 4,993,358, to Mahawili, discloses a chemical vapor deposition (CVD) reactor and method wherein a chamber, preferably configured for receiving a single wafer as a deposition substrate, has multiple gas inlet orifices and exhaust ports which are independently adjustable for dynamically varying and controlling directionality of local gas flow vectors toward and past the deposition substrate.